Among publications on the subject of the preparation of propylene oxide, there are only a few which are concerned with energy integration aspects.
EP 1 293 505 A1 describes a process for the epoxidation of olefins wherein a product stream from the epoxidation reaction which contains olefin, olefin oxide, water-miscible organic solvent, hydrogen peroxide and water, is separated into an overhead product containing olefin, olefin oxide and organic solvent, and into a bottom product containing organic solvent, hydrogen peroxide and water, whereby 20 to 60% of the total amount of organic solvent is removed with the overhead product, and wherein a pre-evaporator with less than 10 theoretical separation stages is used, the separation being carried out at a pressure of 1.5 to less than 3 bar. As the only vague hint to an energy integration aspect, it is stated that there is a possibility to use an integrated heat management in order to improve energy efficiency. In this context, it is disclosed that said pre-evaporator and an optionally present stripper can be heated with the condensation heat of vapors resulting from subsequent distillation stages. In case methanol is used as solvent, a methanol head product having a higher temperature than the bottom temperature of said pre-evaporator and said stripper can be used to heat the pre-evaporator and the stripper. Thus, EP 1 293 505 A1 restricts the heat management to a very specific process in which a pre-evaporator and a stripper are used as apparatuses in an epoxidation process.
WO 02/14298 A1 describes a continuous process for the preparation of an olefinic oxide by direct oxidation of an olefin with hydrogen peroxide. Among other stages, this process comprises feeding a reaction product comprising unreacted hydrogen peroxide, epoxidation reaction by-products, water and reaction solvent into a decomposition zone to decompose hydrogen peroxide. For this purpose, an aqueous basic solution is additionally fed into the decomposition zone. According to a preferred embodiment, a suspension catalyst is used as epoxidation catalyst. In the context of WO 02/14298 A1, it is disclosed that the condensation heat recovered at the top of a specific distillation zone is used to serve at least some of the boiling needs of the process. Into this distillation zone, two streams are fed, one of which is a liquid phase comprising reaction by-products, water and solvent, the other being obtained from a condensation zone and comprising solvent. As to the stages of the overall process and to any specifics about the amounts of the condensation heat is used, WO 02/14298 A1 is silent.
U.S. Pat. No. 6,756,503 B2 relates to a process for producing propylene oxide which comprises reacting propene with hydrogen peroxide in the presence of methanol thus obtaining a mixture comprising propylene oxide, methanol, water and unreacted hydrogen peroxide, separating therefrom a mixture comprising methanol, water and hydrogen peroxide, and separating therefrom water thus obtaining a mixture comprising methanol and methyl formate. It is disclosed that, in case heat recovery is to be realized, two or more distillation columns are preferred. As to any specifics about heat recovery, this document is silent.
WO 2004/074268 A1 discloses a process for the reaction of an organic compound having at least one C-C double bond with hydrogen peroxide in the presence of at least one catalytically active substance and methanol wherein water is separated from a product stream comprising methanol and water and a resulting product stream comprising methanol and at least 3 wt.-% of water is recycled into the process. It is disclosed that a top stream from a distillation column can be used to directly heat up an evaporator in the epoxidation process or in a different process. In the context of WO 2004/074268 A1, it is described that two distillation columns can be used to separate water from above-mentioned mixture wherein the top fractions of both columns are combined to give a product stream having a water content of at least 3 wt.-%. As to any specifics about the stage or the stages said evaporator is used for, this document is silent.
US 2003/146080 A1 describes a process for the production of propylene oxide in the presence of methanol in which propylene oxide is separated from a mixture comprising propylene oxide and methanol, and in which the resulting mixture is worked up wherein methanol is separated from a mixture comprising methanol and methyl formate. It is disclosed that from a mixture comprising methanol and water, water can be separated wherein two distillation columns can be used. It is explicitly described that other process streams can be heated up with the condensation heat obtained at the top of these columns by cooling the condenser of at least one of said columns with water and using the hot water or the steam resulting from cooling.
WO 2004/009572 A1 describes a process for the continuous distillation of a solvent used for the synthesis of an oxirane in which a mixture comprising solvent and resulting from synthesis and subsequent work up is separated in a dividing wall column, wherein the solvent is taken as medium boiling fraction from the side of the dividing wall column. The dividing wall column can be configured as thermally coupled columns which are spatially separated from each other.
WO 2004/009566 A1 discloses a process for the continuously operated distillation of methanol which is used as solvent in a process for producing propylene oxide. It is disclosed that a solvent mixture is separated in a dividing wall column so that a top fraction comprising methanol, a fraction taken from the side comprising methoxy propanols as an azetrope with water, and a bottoms fraction comprising water and propylene glycol are obtained. The methanol obtained as top fraction can be condensed and recycled into the epoxidation process.
Accordingly, the prior art describes either a mere concept concerning the possibility of heat integration or relates to very specific embodiments of epoxidation processes in which not more than one or two stages of the overall process are involved in the heat integration aspect.
Therefore, it is an object of the present invention to provide a highly integrated process for the production of an olefin oxide in which at least three process stages of the overall process are involved with regard to minimization of energy consumption.
It is a further object of the present invention to provide a highly integrated process for the production of an olefin oxide in which the top vapor stream obtained from the separation of methanol from a product stream of the epoxidation process is used to operate evaporators used in at least three process stages of the overall epoxidation process.
It is another object of the present invention to provide a highly integrated process for the production of propylene oxide in which the top vapor stream obtained from the separation of methanol from a product stream of the propene epoxidation process is used to operate evaporators used in at least three process stages of the overall epoxidation process.
It is still another object of the present invention to provide a highly integrated process for the production of an olefin oxide, preferably propylene oxide, in which not only the top vapor stream obtained from the separation of methanol from a product stream of the propene epoxidation process is used to operate evaporators used in at least three process stages of the overall epoxidation process, but in which at least one suitable additional method is employed rendering the process economically and ecologically still more positive concerning the overall energy balance.
It is yet another object of the present invention to provide a highly integrated process for the production of an olefin oxide, preferably propylene oxide, in which above-mentioned advantages are further combined with an optimized, preferably energetically optimized methanol separation.